<!DOCTYPE html>
<html>

<head>
    <meta charset="UTF-8">
    <title></title>
</head>

<body>
    <input type='file' accept='text/plain' onchange='openFile(event)'><br>
    <div id="output"></div>
</body>
<script src="https://cdn.bootcss.com/jquery/3.3.1/jquery.min.js"></script>
<script type="text/javascript">
    var openFile = function (event) {
        var input = event.target;
        var reader = new FileReader();
        reader.onload = function () {
            if (reader.result) {
                //显示文件内容
                $("#output").html(reader.result);
            }
        };
        reader.readAsText(input.files[0]);
    };
</script>

</html>